From Drownings Present as Hypoxic Event in the Journal of Emergency Medical Services:
"One complicating factor in the treatment of a drowning patient is the presence of copious amounts of foam in the upper airway. It was previously thought that this fluid was coming from the lungs, but it’s now recognized that much of it comes from the stomach. Ancient and outdated drowning treatments were directed at “draining” the water from the lungs either through the Heimlich maneuver or inverting the patient. All attempts to suction or clear this foam from the airway only delay much-needed oxygenation and go against most dogma of airway management—the patient is dying from cerebral anoxia and not foam in the upper airways. Thus, prehospital providers should focus on oxygenating and ventilating the patient and not on aggressive suctioning. Of course, if cardiac arrest is present, CPR should be initiated and necessary ALS measures provided."

Parts of an Aquatics International blog posted by Dr. Tom Griffiths relating to this very important subject:
More and more actual drowning scenarios are being caught on security cameras but unfortunately, only lawyers and expert witnesses typically get to see them; water safety advocates who need to see them, don’t. Most of the videos cannot be made public because of confidentiality agreements signed by both parties. But what these videos of actual drownings reveal is surprising, startling, and significant. What these actual drowning videos show us is that we really cannot predict how potential drownees will act when they are fighting for their lives. We worry that if we continue to teach our lifeguards and parents the traditional signs and symptoms of drowning victims that have been taught for decades, they may create a mental picture of a drowning victim that does not match reality. As a result, our teachings may be counterproductive. While some drowning victims do in fact display a vertical posture with head back, weak kick and arms groping just below the surface, many do not. For example, very small children simply drown face down flat, horizontally on the surface with little or no movement. We do agree that drowning is silent and we do agree with the RID Factor. However, more and more security camera footage illustrates that drowning may not be as instinctive as we have been teaching. As Dr. John Hunsaker has stated, “Victims don’t go to Drowning School,” and apparently they have not read our texts. Hopefully as technology grows in swimming pools, we may be able to scrutinize actual drowning footage to better protect people and save lives. Finding these videos and sharing them whenever possible is the first difficult step in the process.